A polybutylene terephthalate (PBT)-series resin is an engineering plastic having various excellent properties such as excellent mechanical properties, electric properties, and shaping processability (or moldability) and is used for a number of applications such as automotive parts and electric or electronic device parts. Moreover, the use of the PBT-series resin as an exterior package or a container material (a housing material) for protecting a substrate has shown an increase. In order to produce such parts, a plurality of molded components are bonded by using a bonding manner (or a bonding method) such as an adhesive, a screw cramp, a snap fit, a hot plate welding, or an ultrasonic welding. However, some problems of these bonding manners are pointed out. For example, in the use of an adhesive, the loss of time for curing of the adhesive, or the burden on the environment becomes a problem. Moreover, in a means using a screw cramp, the labor or the cost required for fastening increases. Further, since a hot plate welding or an ultrasonic welding gives vibration or heat necessary for welding to a product all over, there is a possible damage to the product due to heat or vibration. In contrast, a bonding (or joining) method by laser welding needs to melt only part to be welded of a product. Therefore, the method causes no damage to a product due to heat or vibration involved in the welding, and the welding process is also very simple. Thus, recently the laser welding method has been widely utilized and has attracted attention as a welding manner for various resin components or parts. Furthermore, a resin part (or member) having a metal part (or member) incorporated therein by insert-molding is also used as the resin parts to be subjected to welding. Accordingly, the development of a PBT-series resin having both insert-moldability and high laser-weldability as an insert-molding resin has been expected. Incidentally, the resin properties required for an insert-molded product includes high (or excellent) resistance to large temperature change over a long period of time (resistance to heat shock), that is, heat shock resistance.
It is indicated that the polybutylene terephthalate-series resin is carbonized without substantial laser-welding under laser irradiation due to its low laser transmissivity. Japanese Patent Application laid-Open No. 26656/2001 (JP-2001-26656A, Patent Document 1) discloses a process for producing a united molded product, which comprises uniting a molded product formed from a polyester-series copolymer having a melting point within a specific range with another molded product by a welding processing. This document mentions that a homopolybutylene terephthalate resin has a small laser-welding strength.
Moreover, examples using a polybutylene terephthalate-series resin composition for a metal insert molding are also known. For example, Japanese Patent Application Laid-Open No. 3055/1988 (JP-63-3055A, Patent Document 2) discloses an insert-molded product obtained by insert-molding of a resin composition comprising a polybutylene terephthalate and an acrylic rubber, and a metal or inorganic solid. This document mentions that the acrylic rubber is a rubber-like elastomer obtained by polymerization of an acrylic ester or copolymerization mainly using an acrylic ester and exemplifies a rubber-like polymer which is obtained by graft polymerization of a polymerizable monomer (such as methyl methacrylate) to a polymer obtained by polymerization of an acrylic ester (such as butyl acrylate) and a small amount of a crosslinkable monomer (such as butylene diacrylate). This document also mentions that commercial items, “Kane Ace FM” (manufactured by Kaneka Corporation), “VITAX V-6401” (manufactured by Hitachi Chemical Co., Ltd.), “METABLEN W-300” and “METABLEN W-530” (manufactured by Mitsubishi Rayon Co., Ltd.), and “Acryloid KM-323” and “Acryloid KM-330” (manufactured by Rohm and Haas Company) may be used. Incidentally, this document does not mention laser welding of the above-mentioned resin composition or insert-molded product at all. Even if the composition or product is subjected to laser-welding, it is substantially impossible to produce a laser-welded product because the composition or product has a remarkably low laser transmissivity.
Also, study is in progress to improve the heat shock resistance of a polyester-series resin composition. For example, Japanese Patent Application Laid-Open No. 18166/1995 (JP-7-18166A, Patent Document 3) discloses a thermoplastic polyester resin composition containing (A) 100 parts by weight of a thermoplastic polyester, (B) 5 to 100 parts by weight of a glass fiber, (C) 5 to 100 parts by weight of a glass bead, and (D) 5 to 50 parts by weight of an acrylic rubber. This document mentions that the acrylic rubber (D) is a copolymer of an acrylic ester and a methacrylic ester, the acrylic ester having a saturated or unsaturated straight chain or branched chain aliphatic hydrocarbon having 1 to 5 carbon atom(s) and the methacrylic ester having a saturated or unsaturated straight chain or branched chain aliphatic hydrocarbon group having 1 to 5 carbon atom(s). This document also describes that the brand name “PARALIOD EXL2311” (manufactured by Kureha Chemical Industry, Co., Ltd.) is used in Examples as the acrylic rubber. In addition, this document mentions that a thermoplastic polyester material which has an excellent mechanical property of the thermoplastic polyester and an excellent heat shock resistance is obtained and that the thermoplastic polyester material is effective in inserting or sealing a metal.
Incidentally, these documents have no assumption that these compositions are subjected to laser welding. Moreover, even if the polyester-series compositions described in these documents are subjected to laser-welding, there is a possibility that the compositions cannot substantially be laser-welded due to their low laser transmissivities.
Japanese Patent Application Laid-Open No. 315805/2004 (JP-2004-315805A, Patent Document 4) discloses a laser-weldable polybutylene terephthalate-series resin composition comprising (A) a polybutylene terephthalate-series resin and (B) an elastomer having a refractive index of 1.52 to 1.59. This document mentions that examples of the elastomer include a polystyrene-series elastomer, a polyester-series elastomer, a polyamide-series elastomer, a polyurethane-series elastomer, a polyolefinic elastomer, and others.
[Patent Document 1] JP-2001-26656A (Claims, and Paragraph number [0003])
[Patent Document 2] JP-63-3055A (Claims, and page 2, lower left column, line 12 to page 3, upper left column, line 14)
[Patent Document 3] JP-7-18166A (Claims, and Paragraph numbers [0009], [0018], and [0026])
[Patent Document 4] JP-2004-315805A (Claims, and Paragraph number [0066])